A study dealing with the ground and excited state behavior of arylazirines was initiated. The results obtained indicate that arylazirines undergo photocycloaddition with electron-deficient olefins to give delta 1-pyrroline derivatives. The formation of the cycloadducts was interpreted as proceeding by way of irreversible ring opening of the azirine ring to form a nitrile ylide intermediate, which was subsequently trapped by a suitable dipolarophile. Arylazirines were also found to undergo photodimerization to 1,3-diazabicyclo(3.1.0)hex-3-enes. These dimers undergo subsequent photoreactions. The products formed depend on the substituent groups, the time of irradiation, and the particular solvent employed. Irradiation of arylazirines in the presence of carbon dioxide produces delta 3-oxazolin-5-ones which undergo photoextrusion of carbon dioxide on further irradiation. A kinetic investigation shows that the photochemically generated nitrile ylide does not thermally collapse back to the azirine ring. The chemical behavior of the delta 3-ozazolin-5-one ring was examined in detail.